Synthetic zeolite is a crystalline aluminosilicate and has uniform micropores in an angstrom size resulting from the crystal structure thereof. Taking advantage of this feature, the synthetic zeolite has been industrially used as a molecular sieve adsorbent which adsorbs only the molecules having a specific size, an adsorption separating agent which adsorbs molecules having high affinity, or a catalyst base agent. MTW is a designation representing the framework structure type given to zeolite ZSM-12, and zeolite having the same structure includes CZH-5, NU-13, TPZ-12, Theta-3, and VS-12. The MTW-type zeolite is used in a large amount all over the world at present as a catalyst in petrochemical industry. The feature of the MTW-type zeolite is in that it has 12 membered-ring one-dimensional micropores as described in the following Non Patent Literature 1. Further, the X-ray diffraction pattern showing the structural feature thereof is described in the following Non Patent Literature 2.
Since the MTW-type zeolite has been conventionally produced only by a method in which an organic ammonium ion is used as a structure-directing agent (hereinafter abbreviated as “SDA”), it has been considered that the use of SDA is essential in order to obtain the MTW-type zeolite. Further, since synthesized MTW-type zeolite contains SDA, it has been considered inevitable that the zeolite is fired to remove SDA before it is used.
Various methods for synthesizing the MTW-type zeolite are proposed. A common method is a method of using organic ammonium ions, such as tetraethylammonium ions, methyltriethylammonium ions, or benzyltriethylammonium ions, as SDA. Also, at the same time, addition of alkali metal ions, such as sodium or lithium, is essential. Such a method is for example described in the following Patent Literatures 1 to 3. According to these methods, an MTW-type zeolite having a SiO2/Al2O3 ratio of 20 or more can be obtained. However, the SDAs as described above are expensive, and most SDAs in mother liquor may be decomposed after completion of the crystallization of the MTW-type zeolite. Further, since these SDAs are incorporated into the crystals of the zeolite to be produced, it is necessary to fire the zeolite to remove the SDAs when using the zeolite as an adsorbent or a catalyst. The exhaust gas from the firing causes environmental pollution, and further a large amount of chemicals is required for the detoxification treatment of the synthetic mother liquor containing decomposition products of SDAs. Thus, since the synthetic method of the MTW-type zeolite using SDA is not only expensive, but is a production method having a high environmental load, the realization of a production method in which SDA is not used and an MTW-type zeolite which is obtained by the production method and does not essentially contain organic matter is desired.